Method and Apparatus for Optimizing Radio Resource Control Procedures in Wireless Communication System

ABSTRACT

A method for optimizing a radio resource control procedure in a wireless communication system is disclosed. The wireless communication system supports Coordinated multi-point (CoMP) transmission/reception, which enables a plurality of cells cooperating and providing services for a user equipment (UE). The method includes defining cells directly or indirectly participating in transmission to the UE within the plurality of cells as members of a CoMP cooperating set, and setting the cells of the CoMP cooperating set to use a same system frame number.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/230,741, filed on Aug. 2, 2009 and entitled “Method and apparatus for improving handover in CoMP in a wireless communication system”, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for optimizing a radio resource control (RRC) procedure in a wireless communication system, and more particularly, to a method and apparatus capable of enhancing data rate and throughput of Coordinated multi-point (CoMP) transmission/reception.

2. Description of the Prior Art

Long Term Evolution wireless communication system (LTE system), an advanced high-speed wireless communication system established upon the 3G mobile telecommunication system, supports only packet-switched transmission, and tends to implement both Medium Access Control (MAC) layer and Radio Link Control (RLC) layer in one single communication site, such as in base stations (Node Bs) alone rather than in Node Bs and RNC (Radio Network Controller) respectively, so that the system structure becomes simple.

However, to meet future requirements of all kinds of communication services, the 3rd Generation Partnership Project (3GPP) has started to work out a next generation of the LTE system: the LTE Advanced (LTE-A) system. Coordinated multi-point (CoMP) transmission/reception is introduced into the LTE-A system, and enables adjacent cells cooperating and providing services for a same UE, to improve coverage of high data rates, cell-edge throughput and system throughput. In other words, CoMP transmission/reception can ensure the UE acquiring the same Quality of Service (QoS) in cell center and edge.

In order to realize CoMP transmission, related operating concept, terminology, etc. have been defined in the prior art. For example, for downlink CoMP transmission, definition of a serving cell is as that of LTE system, i.e. a cell for providing Physical Downlink Control Channel (PDCCH) transmission; a CoMP cooperating set indicates all cells directly or indirectly participating in Physical Downlink Shared Channel (PDSCH) transmission.

In addition, many procedures are proposed for optimizing CoMP transmission in the industry. One is applying a serving cell changing procedure (also called handover procedure) without initiating a Random Access (RA) procedure, i.e. an RACH-less handover procedure. First, a handover procedure is utilized for changing a serving cell from a source cell to a target cell when a UE moves or a network terminal tends to change configuration of the UE. After the handover procedure is initiated, the UE needs to perform a RA procedure, for performing uplink synchronization with the target cell and acquiring uplink grant for sending back a complete message. As the above description, CoMP transmission can enhance data rate or improve cell-edge throughput. In other words, except for enhancing data rate, another reason to apply CoMP transmission is to improve transmission of UE in cell edge. In such a situation, the handover procedure is likely to be frequently triggered. Moreover, once the RA procedure is initiated, a period of time is required for completing the RA procedure, during which no data or only a few data can be transmitted; thus, data transmission rate is affected.

Reasons to apply the RACH-less handover procedure in CoMP transmission are as follows: first, since Timing Advances (TAs) of all cells within a same CoMP cooperating set are the same or similar, uplink of the UE may be still synchronized after the UE is handed over to the target cell if the target cell is within the same CoMP cooperating set, and thus the RA procedure for performing uplink synchronization is not necessary; second, other than performing the RA procedure for acquiring the uplink grant, the UE can perform a scheduling request procedure for acquiring a uplink grant for sending back a complete message.

When the RACH-less handover procedure is applied, delay of the handover procedure can be effectively reduced, so as to maintain or enhance data rate. However, in order to perform scheduling request, the UE needs to acquire a System Frame Number (SFN) of the target cell first, so as to recognize scheduling request resource assigned by the network terminal, and apply scheduling request configuration. The SFN is included in a system information message MasterInformationBlock, which is a message periodically broadcasted by the network terminal. In other words, when the UE tends to perform the scheduling request after changing the serving cell to target cell, the UE needs to wait for the system information message MasterInformationBlock broadcasted by the network terminal first, and thus acquires the SFN. In addition, after the UE completes the handover procedure, the UE still needs to apply many measurement or radio resource configurations related to the SFN, such as measurement gap, periodic channel quality indicator (CQI) reporting, sounding reference symbol (RS), etc.

In short, when CoMP transmission is applied, if the system uses the RACH-less handover procedure, the UE needs to perform the scheduling request procedure to acquire an uplink grant, and use the acquired uplink grant to send back the complete message, to complete the handover procedure. However, the scheduling request procedure is related to the SFN, which is included in the system information message MasterInformationBlock periodically broadcasted by the network terminal. Therefore, completing time of the handover procedure is related to acquiring time of the SFN. Meanwhile, applying related measurement or radio resource configurations after the handover procedure is completed is related to the SFN as well. In other words, the acquiring time of the SFN affects the completing time of handover procedure, and affects the applying time of related measurement or radio resource configurations after the handover procedure is completed. An objective of CoMP transmission is to enhance data rate; however, data rate, throughput, etc. are affected and reduced if the UE delays the completing time of the handover procedure or the applying time of measurement and radio resource configurations due to waiting for the SFN. Thus, how to improve the handover procedure when CoMP transmission is applied has become an issue in the industry.

SUMMARY OF THE INVENTION

It is therefore an objective of the present invention to provide a wireless communication system a method and apparatus for optimizing a radio resource control (RRC) procedure.

The present invention discloses a method for optimizing a radio resource control (RRC) procedure in a wireless communication system. The wireless communication system supports Coordinated multi-point (CoMP) transmission/reception, which enables a plurality of cells cooperating and providing services for a UE. The method includes steps of defining cells of the plurality of cells directly or indirectly participating in transmission to the UE as members of a CoMP cooperating set, and setting the cells of the CoMP cooperating set to use a same System Frame Number (SFN).

The present invention further discloses a communication device for optimizing a radio resource control (RRC) procedure in a wireless communication system. The wireless communication system supports Coordinated multi-point (CoMP) transmission/reception, which enables a plurality of cells cooperating and providing services for a UE. The communication device includes a processor for executing a program; and a memory coupled to the processor for storing the program. The program includes steps of defining cells of the plurality of cells directly or indirectly participating in transmission to the UE as members of a CoMP cooperating set, and setting the cells of the CoMP cooperating set to use a same System Frame Number (SFN).

The present invention further discloses a method for optimizing a radio resource control (RRC) procedure in a wireless communication system. The method includes steps of receiving a RRC message to initiate the RRC procedure, for changing a serving cell from a source cell to a target cell, and using a first System Frame Number (SFN) of the source cell as a second SFN of the target cell.

The present invention further discloses a communication device for optimizing a RRC procedure in a wireless communication system. The communication device includes a processor for executing a program, and a memory coupled to the processor for storing the program. The program includes steps of receiving a RRC message to initiate the RRC procedure, for changing a serving cell from a source cell to a target cell, and using a first System Frame Number (SFN) of the source cell as a second SFN of the target cell.

These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a wireless communications system.

FIG. 2 is a function block diagram of a wireless communications device.

FIG. 3 is a diagram of a program of FIG. 2.

FIG. 4 is a flowchart of a process according to an embodiment of the present invention.

FIG. 5 is a flowchart of another process according to an embodiment of the present invention.

DETAILED DESCRIPTION

Please refer to FIG. 1, which illustrates a schematic diagram of a wireless communication system 10. The wireless communication system 10 is preferably an LTE advanced (LTE-A) system, and is briefly composed of a network and a plurality of user equipments (UEs). In FIG. 1, the network and the UEs are simply utilized for illustrating the structure of the wireless communication system 10. Practically, the network may comprise a plurality of base stations (Node Bs), radio network controllers and so on according to actual demands, and the UEs can be devices such as mobile phones, computer systems, etc.

Please refer to FIG. 2, which is a functional block diagram of a communication device 100 in a wireless communication system. The communication device 100 can be utilized for realizing the network or the UEs in FIG. 1. For the sake of brevity, FIG. 2 only shows an input device 102, an output device 104, a control circuit 106, a central processing unit (CPU) 108, a memory 110, a program 112, and a transceiver 114 of the communication device 100. In the communication device 100, the control circuit 106 executes the program 112 in the memory 110 through the CPU 108, thereby controlling an operation of the communication device 100. The communication device 100 can receive signals input by a user through the input device 102, such as a keyboard, and can output images and sounds through the output device 104, such as a monitor or speakers. The transceiver 114 is used to receive and transmit wireless signals, deliver received signals to the control circuit 106, and output signals generated by the control circuit 106 wirelessly. From a perspective of a communication protocol framework, the transceiver 114 can be seen as a portion of Layer 1, and the control circuit 106 can be utilized to realize functions of Layer 2 and Layer 3.

Please continue to refer to FIG. 3. FIG. 3 is a diagram of the program 112 shown in FIG. 2. The program 112 includes an application layer 200, a Layer 3 202, and a Layer 2 206, and is coupled to a Layer 1 218. The Layer 3 202 performs radio resource control. The Layer 2 206 comprises a Radio Link Control (RLC) layer and a Medium Access Control (MAC) layer, and performs link control. The Layer 1 218 performs physical connections.

The LTE-A system introduces a coordinated multi-point (CoMP) transmission/reception technology, which enables adjacent cells cooperating and providing services for a same UE to improve coverage of high data rates and cell-edge or system throughput. In such a situation, the embodiment of the present invention provides a RRC procedure optimizing program 220, for optimizing operating time of an RRC procedure. The RRC procedure can be a handover procedure or a radio resource reconfiguration procedure, for changing a serving cell of the UE from a source cell to a target cell.

Please refer to FIG. 4, which is a schematic diagram of a procedure 40 according to an embodiment of the present invention. The procedure 40 is utilized in a network terminal of the wireless communication system 10, and can be compiled into the RRC procedure optimizing program 220. The wireless communication system 10 has configured CoMP transmission/reception, and enables a plurality of cells cooperating and providing services for a UE. The procedure 40 includes the following steps:

Step 400: Start.

Step 402: Define cells directly or indirectly participating in transmission to the UE within the plurality of cells as members of a CoMP cooperating set.

Step 404: Set the cells of the CoMP cooperating set to use a same SFN.

Step 406: End.

According to the procedure 40, the network terminal sets all cells of the CoMP cooperating set to use the same SFN according to an embodiment of the present invention. As a result, if the wireless communication system 10 applies the RACH-less handover procedure, the UE can use the SFN of the source cell when the UE is handed over within the CoMP cooperating set, so as to initiate a scheduling request procedure for acquiring an uplink grant, and complete the handover procedure after using the acquired uplink grant to send back a complete message. In such a situation, since the UE does not need to wait for the SFN broadcasted by the network terminal, completing time of the handover procedure is significantly reduced, so is applying time of related measurement or radio resource configuration after the handover procedure is completed.

In short, via the procedure 40, the network terminal sets all the cells of the CoMP cooperating set to use the same SFN, such that the UE does not need to wait for the SFN when the UE is handed over within the CoMP cooperating set, which reduces the completing time required by the handover procedure. Preferably, the CoMP cooperating set is controlled by a same eNB, the SFN is broadcasted by the network terminal through a system information message MasterInformationBlock, and measurement or radio resource configuration applied by the UE after the handover procedure is completed can be configurations such as a measurement gap, a periodic channel quality indicator (CQI) reporting, a sounding reference symbol (RS), a scheduling request, etc.

On the other hand, for operations of the UE, please refer to FIG. 5, which is a schematic diagram of a procedure 50 according to an embodiment of the present invention. The procedure 50 is utilized in a UE of the wireless communication system 10, and can be complied into the RRC procedure optimizing program 220. The procedure 50 includes the following steps:

Step 500: Start.

Step 502: Receive an RRC message to initiate the RRC procedure, for changing a serving cell from a source cell to a target cell.

Step 504: Use a first SFN of the source cell as a second SFN of the target cell.

Step 506: End.

According to the procedure 50, if the UE receives an RRC message for initiating an RRC procedure, which is utilized for changing the serving cell from the source cell to the target cell, the UE uses the SFN of the source cell as the SFN of the target cell, i.e. still using the SFN of the source cell as the SFN of the target cell. In such a situation, since the SFN of the target cell is the same with the SFN of the source cell, the UE does not need to wait for receiving system information broadcasted by the network terminal, which reduces the completing time of the RRC procedure or the applying time of related measurement or radio resource configuration.

Preferably, the RRC message is an RRCConnectionReconfiguration message; the source cell and the target cell are within the CoMP cooperating set; the source cell and the target cell are both controlled by a same eNB; and measurement or radio resource configuration applied by the UE after the RRC procedure is completed can be configuration such as a measurement gap, a periodic CQI reporting, a sounding RS or a scheduling request, etc.

Therefore, if the wireless communication system 10 applies the RACH-less handover procedure, the UE can use the SFN of the source cell when the UE is handed over within the CoMP cooperating set, so as to initiate a scheduling request procedure for acquiring uplink grant, and complete the handover procedure after using the acquired uplink grant to send back a complete message. In such a situation, since the UE does not need to wait the SFN broadcasted by the network terminal, completing time required by the handover procedure is significantly reduced, so is applying time of related measurement or radio resource configurations after the handover procedure is completed.

Noticeably, using the SFN of the source cell as the SFN of the target cell in the step 504 needs to cooperate with operations of the network terminal. For example, the network terminal can set all the cells of the CoMP cooperating set to use the same SFN according to the procedure 40. Or, the network terminal can add an indication signal within the RRC message, for indicating whether the SFN of the source cell is identical to the SFN of the target cell; if the SFN of the source cell is identical to the SFN of the target cell, the UE can use the SFN of the source cell as the SFN of the target cell.

Noticeably, the above realization of the steps in the processes 40, 50 should be well known by those skilled in the art. For example, the steps of the processes 40, 50 can be compiled as units into the RRC procedure optimizing program 220 by instructions, parameters, variables, etc. of specific programming languages.

To sum up, for CoMP transmission, if a system uses the RACH-less handover procedure, and the UE is handed over within the CoMP cooperating set, the UE can use the SFN of the source cell according to the embodiment of the present invention, to reduce the completing time required by the handover procedure and the applying time of measurement or radio resource configurations after the handover procedure is completed. As a result, the present inventions can enhance data transmission rate, throughput, etc. of CoMP transmission.

Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims. 

1. A method for optimizing a radio resource control (RRC) procedure in a wireless communication system, the wireless communication system supporting Coordinated multi-point (CoMP) transmission/reception, which enables a plurality of cells cooperating and providing services for a UE, the method comprising: defining cells directly or indirectly participating in transmission to the UE within the plurality of cells as members of a CoMP cooperating set; and setting the cells of the CoMP cooperating set to use a same System Frame Number (SFN).
 2. The method of claim 1, wherein the SFN is broadcasted by a system information message.
 3. The method of claim 2, wherein the cells of the CoMP cooperating set are controlled by a same Node B of the network terminal.
 4. The method of claim 1, wherein the RRC procedure is utilized for changing a serving cell corresponding to the UE from a source cell to a target cell.
 5. A communication device for optimizing a radio resource control (RRC) procedure in a wireless communication system, the wireless communication system supporting Coordinated multi-point (CoMP) transmission/reception, which enables a plurality of cells cooperating and providing services for a UE, the communication device comprising: a processor for executing a program; and a memory coupled to the processor for storing the program; wherein the program comprises: defining cells directly or indirectly participating in transmission to the UE within the plurality of cells as members of a CoMP cooperating set; and setting the cells of the CoMP cooperating set to use a same System Frame Number (SFN).
 6. The communication device of claim 5, wherein the SFN is broadcasted by a system information message.
 7. The communication device of claim 6, wherein the cells of the CoMP cooperating set are controlled by a same Node B of the network terminal.
 8. The communication device of claim 5, wherein the RRC procedure is utilized for changing a serving cell corresponding to the UE from a source cell to a target cell.
 9. A method for optimizing a radio resource control (RRC) procedure in a wireless communication system, the method comprising: receiving an RRC message to initiate the RRC procedure, for changing a serving cell from a source cell to a target cell; and using a first System Frame Number (SFN) of the source cell as a second SFN of the target cell.
 10. The method of claim 9 further comprising applying at least one measurement or radio resource configuration according to the first SFN.
 11. The method of claim 10, wherein the at least one measurement or radio resource configuration is selected from a measurement gap, a periodic channel quality indicator (CQI) reporting, a sounding reference symbol (RS) or a scheduling request configuration.
 12. The method of claim 9, wherein the RRC message comprising an indication signal, for indicating whether the first SFN is identical to the second SFN.
 13. The method of claim 12, wherein using the first SFN of the source cell as the second SFN of the target cell is using the first SFN as the second SFN when the indication signal indicates the first SFN is identical to the second SFN according to the indication signal in the RRC message.
 14. The method of claim 9, wherein the RRC procedure does not need to initiate a random access procedure.
 15. The method of claim 9, wherein the source cell and the target cell are within a CoMP cooperating set, which comprises cells of a plurality of cells directly or indirectly participating in transmission to the UE.
 16. The method of claim 9, wherein the source cell and the target cell are controlled by a same Node B of the network terminal.
 17. The method of claim 9, wherein the RRC message is an RRCConnectionReconfiguration message.
 18. The method of claim 9, wherein the RRC procedure is a handover procedure or a radio resource reconfiguration procedure.
 19. A communication device for optimizing a RRC procedure in a wireless communication system, the communication device comprising: a processor for executing a program; and a memory coupled to the processor for storing the program; wherein the program comprises: receiving an RRC message to initiate the RRC procedure, for changing a serving cell from a source cell to a target cell; and using a first System Frame Number (SFN) of the source cell as a second SFN of the target cell.
 20. The communication device of claim 19, wherein the program further comprises applying at least one measurement or radio resource configuration according to the first SFN.
 21. The communication device of claim 20, wherein the at least one measurement or radio resource configuration is selected from a measurement gap, a periodic channel quality indicator (CQI) reporting, a sounding reference symbol (RS) or a scheduling request configuration.
 22. The communication device of claim 19, wherein the RRC message comprises an indication signal, for indicating whether the first SFN is identical to the second SFN.
 23. The communication device of claim 22, wherein using the first SFN of the source cell as the second SFN of the target cell is using the first SFN as the second SFN when the indication signal indicates the first SFN is identical to the second SFN according to the indication signal in the RRC message.
 24. The communication device of claim 19, wherein the RRC procedure does not need to initiate a random access procedure.
 25. The communication device of claim 19, wherein the source cell and the target cell are within a CoMP cooperating set, which comprises cells of a plurality of cells directly or indirectly participating in transmission to the UE.
 26. The communication device of claim 19, wherein the source cell and the target cell are controlled by a same Node B of the network terminal.
 27. The communication device of claim 19, wherein the RRC message is an RRCConnectionReconfiguration message.
 28. The communication device of claim 19, wherein the RRC procedure is a handover procedure or a radio resource reconfiguration procedure. 